Download visual field defects in optic chiasm lesions

CLINICAL ASPECTS
VISUAL FIELD DEFECTS IN OPTIC CHIASM LESIONS
MARIETA DUMITRACHE1, RODICA LASCU2
1
Ophthalmological Emergency Clinical Hospital, Bucureşti, 2Emergency Clinical County Hospital, Sibiu
Keywords: bitemporal
defect-quadrantic
or
hemianopic,
Wilbrand’knee,
junctional
scotoma,
bitemporal hemianopic
scotomas, arcuate defect
Abstract: Temporal visual field defects result from the compression of the optic chiasm medially
involving the crossing of nasal retinal fibres, while nasal visual field defects occur with lateral optic
chiasm compression involving the temporal retinal fibres. The visual field defects reported with optic
chiasm compression include nasal visual field loss, arcuate visual field defects, scotomatous visual field
defects and homonymous visual field loss, in addition to the typical temporal visual field loss.
Cuvinte cheie: defect
bitemporal-cvadrantic
sau
hemianopic,
genunchiul lui Wilbrand,
scotom
joncţional,
scotoame hemianopice
bitemporale,
defect
arcuat
Rezumat: Defectele câmpului vizual temporal rezultă de la compresiunea chiasmei optice implicând
medial încrucişarea fibrelor retiniene nazale, în timp ce defectele câmpului vizual nazal apar cu
compresia chiasmei optice laterale implicând fibrele retiniene temporale. Defectele câmpului vizual
raportate cu compresia chiasmei optice includ pierderea câmpului vizual nazal, defecte ale câmpului
vizual arcuat, defecte câmp vizual scotoame şi pierderea câmpului vizual omonim, pe lângă pierderea
câmpului vizual temporal tipic.
„Rules of the road” for the optic chiasm:
Three rules describe the course of major fibres bundles
in the chiasm:
•
The nasal retinal fibres (including the nasal half of the
macula) of each eye cross in the chiasm to the contralateral
optic tract. Temporal fibres remain uncrossed. Thus, a
chiasmal lesion will cause a bitemporal hemianopia due to
interruption of decussating nasal fibres.
•
Lower retinal fibres project through the optic nerve and
chiasm to lie laterally in the tracts; upper retinal fibres will
lie medially (there is a 90-degree rotation of fibres from the
nerves through the chiasm into the tracts)
•
Inferonasal retinal fibres cross into the chiasm and cross
anteriorly approximately 4 mm in the contralateral optic
nerve (Wilbrand ́s knee) then redress back in to opposite
optic tract. The existence of Wilbrand ́s knee is
controversial.
•
„Macular” crossing fibres are distributed throughout the
chiasm and if primarily affected, cause a „central”
bitemporal hemianopia.
•
Clinical “pearl”: if a patient comes in with poor vision in
the left eye, the important eye for visual examination is the
right due to the involvement of Wilbrand‘s knee. The
lesion is now intracranial at the junction of the left optic
nerve and chiasm. The field defects constitute a junctional
scotoma.
Although there are many variations in the visual field
defects caused by the damage to the optic chiasm, the essential
feature is some type of bitemporal defect, the hallmark of
damage to fibres that cross within the chiasm. The bitemporal
defects may be superior, inferior, or complete, and they may be
peripheral, central, or both. Many lesions that arise in the region
of the chiasm affect not only the entire chiasm but also the
intracranial optic nerves. Most visual field defects produced by
lesions that damage the optic chiasm seem to result from the
damage at one of three locations: (a) the anterior angle of the
chiasm, (b) the body of the chiasm, or (c) the posterior angle of
the chiasm.
Lesions that damage the body of the optic chiasm
The lesions that damage the body of the optic chiasm
produce a bitemporal defect that may be quadrantic or
hemianopic and that may be peripheral, central, or both, with or
without the so-called „splitting of the macula”. In most cases,
visual acuity is normal. In some patients, however, visual acuity
is diminished and a bitemporal hemianopia is present. When the
lesion compresses the chiasm from below, such as occurs with a
pituitary adenoma, the field defects are typical. When the
peripheral fibres are principally affected, the field defects
usually commence in the outer upper quadrants of both eyes. In
the field of the right eye, the defect usually progresses in a
clockwise direction and in the left eye in a counterclockwise
direction. Alternatively, suprasellar, suprachiasmal compressive
lesions-such
as
tuberculum
sellae
meningiomas,
craniopharyngiomas, aneurysms, and dolichoectatic anterior
cerebral arteries-may damage the superior fibers of the optic
chiasm, as may infiltrating lesions such as benign and malignant
gliomas, and cavernous angiomas. The defects in the visual
fields in such cases are still bitemporal, but are located in the
inferior rather than the superior fields of both eyes. Papilledema,
which is quite unusual in patients with suprasellar, infrachiasmal
lesions, is somewhat more common in suprachiasmal lesions
because such lesions can extend into the 3rd ventricle.
Lesions that damage the posterior angle of the
optic chiasm
1
Corresponding author: Rodica Lascu, Str. Aleea Infanteriştilor, Bloc I, Scara B, Etaj III, Ap.25, Sibiu, România; e-mail: [email protected];
tel +40-720547341
Article received on 26.01.2012 and accepted for publication on 23.03.2012
ACTA MEDICA TRANSILVANICA June 2012;2(2):185-187
AMT, v. II, no. 2, 2012, p. 185
CLINICAL ASPECTS
Lesions that damage the posterior aspect of the optic
chiasm produce characteristic defects in the visual fields:
bitemporal hemianopic scotomas. Such defects may be
cecocentral scotomas and attributed to a toxic, metabolic, or
even hereditary process rather than to a tumour. True bitemporal
hemianopic scotomas are almost always associated with normal
visual acuity and colour perception, whereas cecocentral
scotomas are invariably associated with reduced visual acuity
and dyschromatopsia. Lesions that damage the posterior aspect
of the optic chiasm may also damage one of the optic tracts, thus
producing an homonymous field defect that is combined with
whatever field defect has occurred from damage to the optic
chiasm. Bitemporal homonymous scotomas are important in
localizing a lesion.
Visual Field Defects Caused by Lesions That Damage the
Optic Chiasm after Initially Damaging the Optic Nerve or
Optic Tract
If there is extension of a lesion from the optic nerve or
the optic tract to the optic chiasm, the blind eye usually is on the
side of the lesion. When there is extension of a lesion from an
optic nerve or optic tract to the optic chiasm, the blind (or nearblind) eye is always on the side of the original lesion, and when
there is extension of a lesion from the optic chiasm to the optic
nerve or to the optic tract, the blind (or near-blind) eye is always
on the side of the extension of the lesion.
The degree of visual field loss is usually asymmetrical.
Optic atrophy is only present in 50% of cases with visual field
defects. For this reason, it is extremely important to perform
careful examination of the visual fields in all patients with
unexplained visual loss.
Compression of the optic chiasm may be symmetrical
or asymmetrical relating to the size of lesion and its degree of
involvement of the optic chiasm, optic nerve and optic tract.
Symmetrical or asymmetrical compression is reflected by the
presence of bilateral or unilateral visual field defects.
At the junction of the optic nerve and optic chiasm, the
crossed and uncrossed retinal nerve fibres are separated;
consequently, a small lesion of the optic nerve at this level
affecting either the crossed or the uncrossed fibres may give rise
to a unilateral hemianopic defect. The involvement of the
ipsilateral optic nerve close enough to the optic chiasm (to
impair selectively conduction in crossing nasal retinal fibres
from the ipsilateral eye, but too anterior to affect the crossing
nasal retinal fibres from the contralateral eye) produces
monocular temporal hemifield loss. Junctional scotoma:
temporal hemianopsic central scotoma associated with
deficiency in opposite superior temporal quadrant, situation
described by Traquir. Junctional scotoma presents a lesion
placed in inside angle, anterior of chiasm. The junction scotoma
is met particularly in tumours of the anterior angle of chiasm at
the junction between the optic nerve and the chiasm. The
suffering of these fibres at the junction between the optic nerve
and chiasm, that is the suffering of the „anterior knee”, produces
a superior temporal peripherial deficiency, to the opposite eye.
The fibres from the nasal inferior quadrant of the retina go
through the anterior part of the chiasm, those coming from the
superior nasal quadrants go through the posterior side of the
chiasm. That is why pituitar tumours produce initially
deficiencies in the superior temporal quadrant, and the
craniopharyngiomas produce initially deficiencies in the inferior
temporal field.
Arcuate visual field defects have been proposed to
result from vascular changes in the optic nerve rather than at the
optic chiasm. Compression of the optic nerve at the anterior
optic chiasm level might also explain the presence of an arcuate
defect. Trobe (1974) described hemianopic temporal arcuate
visual field defects due to a lesion in the anterocentral optic
chiasm, where crossing and non-crossing portions of the nerve
fibre bundles separate; the lesion would selectively impair
crossing fibres.
Bitemporal
hemianopic
central
scotomas
(heteronimous) are caused by a lesion strictly placed at chiasm,
particularly on its posterior edge. The unilateral central scotoma
sometimes expresses a compression lesion: tumour of sellar
area, meningioma of olfactory ditch. The bilateral central
scotoma is mentioned among different types of visual troubles
during the optochiasma arachnoid. Hemianopia is a bilateral
deficiency of visual field, representing an alteration of the
pathways from the optic chiasm up to occipital cortex. With
reference to the place of lesion, hemianopic deficiencies present
different aspects which have a very important significance if
neuropathological diagnosis. Bitemporal hemianopia is met in
sagittal lesion of chiasm, in pituitary adenoma,
craniopharyngiomas, gliomas of optic chiasm, optochiasmal
arahnoid, tubersellar meningiomas, obstructive hydrocephalus
with chiasmatic compression by the bottom of the third
ventricle, carotid aneurysms situated in sellar, anterior cerebral
aneurysms, craniocerebral trauma with chiasm involvement.
When we come across a temporal hemianopic
deficiency to an eye and blindness to the other, it is difficult to
state the chiasmatical origin of the lesion. It is possible that, by
means of a big index or by using a candle in an obscure room,
we can observe the presence of temporal retinal sensitivity of
the atrophy of the eye and the absence of it in the nasal retinal
area. Binasal heteronymous hemianopia is the loss of both nasal
half fields, corresponding to the lesion of the fibres of temporal
half retinas. The lesion focuses on the temporal uncrossed direct
bundle at the chiasm level (in lateral lesion of the chiasm).
CRANIOPHARYNGIOMA
Sometimes hemianopia appears as a result of the
compression of the optic pathway by tumour of sellar area
(craniopharyngiom).Visual
field
defects
with
craniopharyngiomas are frequently asymmetric bitemporal
hemianopias or a homonymous pattern with reduced acuity. The
craniopharyngiomas will not only cause inferotemporal field
defects but also bitemporal hemianopic scotomas. Situations
starting with homonim hemianopic central scotomas and
paradoxal situations of homonim hemianopic with sparing of the
macula are quoted.
Figure no. 1. Humphrey perimeter visual field assessment:
craniopharyngioma. Bitemporal hemianopia is present with
some superior nasal visual field impairment also present
bilaterally.
AMT, v. II, no. 2, 2012, p. 186
CLINICAL ASPECTS
directly above the sella. As the tumour grows upwards it splays
GLIOMA AND MENINGIOMA
the anterior chiasmal notch and compresses the crossing
Meningiomas compressing the junction of the optic
inferonasal fibres, causing a defect in the upper visual field.
chiasm and optic nerve will interfere with the anterior knee of
With further tumour extension, the defect progresses in an
Wilbrand. A lesion at this site will therefore give rise to an
anticlockwise direction in the left eye and clockwise in the right
ipsilateral central scotoma and a contralateral upper temporal
eye to involve the lower visual field.
field defect (junctional scotoma). For this reason, it is very
important to test the visual field of the opposite eye in all
patients who present unexplained unilateral visual impairment,
Figure no. 3. Humphrey perimeter visual field assessment:
particularly including a central visual field defect.
pituitary adenoma. There is superior temporal visual field
Visual deficits due to meningiomas and gliomas
impairment (left greater than right) due to involvement of
usually take the form of slowly progressive monocular loss of
the inferior retinal nerve fibres first. Note the decibel values
vision. When both fields are involved, there is a distinct
and probability plots.
tendency toward marked asymmetry.
HYDROCEPHALUS
The optic chiasm is situated in the anteroinferior region of
the third ventricle. An enlarged third ventricle due to raised
intracranial pressure may press on the superior aspect of the chiasm
resulting in a visual deficit of the inferior quadrants initially.
Figure no. 2. Humphrey perimeter visual field assessment:
hydrocephalus. There is severe impairment of visual field,
but particularly loss in the temporal visual field as evident
on the pattern deviation plot and corrected pattern standard
deviation plot. Note the decibel values for the bitemporal
areas of the visual fields.
VASCULAR ABNORMALITIES
Nasal visual field defects may also be caused by
arterial aneurysms. A dilatation of an internal carotid aneurysm
may cause lateral compression of the optic chiasm. The field
defect is usually unilateral, but may be bilateral with large
aneurysms or bilateral carotid aneurysms.
1.
2.
3.
MULTIPLE SCLEROSIS
This may commence with a central scotoma which
progresses to hemianopic scotoma.
PITUITARY ADENOMA
Bitemporal visual field defects are classically
associated with optic chiasm compression. The inferonasal
retinal nerve fibres cross low and anteriorly, and therefore are
most vulnerable to damage from expanding sellar lesions,
typically pituitary adenomas.
Compression of the optic chiasm may be
asymmetrical, thus causing an asymmetrical visual field defect
such that temporal visual field loss is present in one eye but the
other eye can have very little involvement. With extensive
compression of the optic chiasm, there can be substantial loss of
visual field.
In approximately 10% of normal subjects, the optic
chiasm is situated more anteriorly over the tuberculum sellaeprefixed (Walsh and Hoyt 1982). In this situation, pituitary
tumours may compress the optic tract first, resulting in
homonymous defects (Trobe1974). Elkington (1968) reported
that homonymous hemianopia is uncommon, but is particularly
associated with large and extensive tumours.
In about 80% of normal subjects, the optic chiasm lies
4.
5.
6.
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